1. Field of the Invention
The present invention relates to a root canal filling material that is used for the root canal treatment in the dental therapy. More particularly, the invention relates to a root canal filling material that is usually formed in a point-like state and provided, is not bent when inserted into the root canal, and is extremely good in filling properties within the root canal.
2. Description of the Conventional Art
In order to carry out the therapy of dental pulp disease and apical periodontitis, is taken a treatment in which a substance that is materially stable is filled in the root canal after extirpation of dental pulp, thereby keeping a tooth root harmless to a periodontal tissue. At this time, the filling material to be filled within the root canal, that is stable to living bodies, is a root canal filling material. At present, of those root canal filling material, is most widely used a point-like filling material called a gutta-percha point. This filling material is composed mainly of gutta-percha as a natural resin and zinc white. Since this filling material is stable to living bodies, it is widely used as a root canal filling material.
While the method for carrying out the root canal filling using this gutta-percha point includes various methods, a filling method called a lateral condensation method is most commonly spread. This lateral condensation method is achieved by using two types of gutta-percha points having a different thickness from each other (a master point and an accessory point). In this filling method, the master point is first filled, and the accessory point is then filled, thereby filling a gap, i.e., the gutta-percha points are filled while applying a pressure.
However, the root canal is not always simple in shape and is often curved. For this reason, the gutta-percha point is required to have a hardness to some extent and to be resistant to the pressure applied when inserted into the root canal. But, when the hardness of the gutta-percha point is increased excessively, the point per se is likely broken, and it is difficult that the point reaches near the root apex. As a result, the root canal filling has been liable to be incomplete.
Further, when the gutta-percha point is inserted within the root canal, there is employed an operation for minutely filling the gutta-percha point by repeating the procedures in which the gutta-percha point is brought into press contact with a metallic long and slender instrument called a spreader and deformed slightly. However, in this filling operation, when the gutta-percha point is not deformed properly, it is very difficult to achieve the filling by the spreader. As a result, not only the filling rate of the gutta-percha point within the root canal has been lowered, but also there has been a possibility to induce a change of a morbid state caused by the generation of a gap. In addition, the adhesion between the gutta-percha points each other, or between the gutta-percha point and the root canal wall during the press contact is insufficient. As a result, the sealing properties have been poor so that a change of a morbid state has been possibly induced, too. Moreover, in order to facilitate the confirmation by X-rays, it is one of important characteristics required for the root canal filling material to impart sufficient radiopacity to the root canal filling material.
Thus, the present invention is aimed at developing a root canal filling material to be usually formed in a point-like state and provided, which is higher in strength than gutta-percha point currently used for root canal filling, is hardly broken, is easy for root canal filling operation, is properly deformed during press contact, is high in adhesion and superior in sealing properties between root canal filling material each other, or between a root canal filling material and a root canal wall, and is provided with proper radiopacity.
The root canal filling material that is used in the present invention is a root canal filling material comprising one or two or more thermoplastic resins selected from trans-polyisoprene, polyethylene, polypropylene, and a copolymer of polyethylene and polypropylene, to which are added a styrene block copolymer as a component for not only improving the breakage resistance but also improving the adhesion during press contact; a paraffin wax as a component for imparting proper plasticity; and one or two or more inorganic fillers selected from zinc oxide, barium sulfate, zirconium oxide, and titanium oxide, as a component for imparting proper hardness and radiopacity within the root canal.
Specifically, the present invention is concerned with a root canal filling material comprising (A) 1 to 50% by weight of one or two or more thermoplastic resins selected from trans-polyisoprene, polyethylene, polypropylene, and a copolymer of polyethylene and polypropylene; (B) 0.1 to 20% by weight of a styrene block copolymer; (C) 0.1 to 10% by weight of a paraffin wax; and (D) 30 to 95% by weight of one or two or more inorganic fillers selected from zinc oxide, barium sulfate, zirconium oxide, and titanium oxide.
In the root canal filling material according to the present invention, the component (A) is a component for imparting basic strength and formability as the root canal filling material. Of the thermoplastic resins as the component (A), trans-polyisoprene is a thermoplastic resin, which is present as a major component of gutta-percha as a natural resin, has slight rubber elasticity, and is softened at about 70xc2x0 C. On the other hand, polyethylene, polypropylene, and the copolymer of polyethylene and polypropylene are a resin generally used in films and various moldings. Since these thermoplastic resins are generally made into a hard molding but do not have rubber elasticity very much, they are a material that has hitherto been not able to be used for the root canal filling material required to have proper flexibility. However, it has become possible to impart proper flexibility, plasticity, and filling properties when combined with the component (B) and the component (C) as described later.
The component (A) is one or two or more thermoplastic resins selected from trans-polyisoprene, polyethylene, polypropylene, and a copolymer of polyethylene and polypropylene. It is necessary that the content of the component (A) is 1 to 50% by weight. When the content of the component (A) is less than 1% by weight, not only it is impossible to impart sufficient strength to the root canal filling material, but also the root canal filling material is very brittle, and it is difficult to achieve the filling operation within the root canal. On the other hand, when the content of the component (A) exceeds 50% by weight, since the amount of the inorganic filler as the component (D) to be compounded as described later, is small, the radiopacity is lowered so that it becomes difficult to undergo the confirmation by X-rays.
The component (B) is a component for imparting the characteristic features of the present invention, i.e., the root canal filling material is hardly broken during the root canal filling operation, and the adhesion between the root canal filling material each other, or between the root canal filling material and the root canal wall during the press contact is enhanced. For the styrene block copolymer as the component (B), can be used a block copolymer of polystyrene and polybutadiene, a block copolymer of polystyrene and polyisoprene, and a block copolymer of polystyrene and a polyolefin. Since the component (B) per se has elasticity as in vulcanized rubbers, when used together with the component (A), it becomes possible to impart proper flexibility, thereby imparting a characteristic that the root canal filling material is hardly broken during the root canal filling.
In addition, when the component (B) is used together with the component (C) as described later, not only the adhesion between the root canal filling material each other, or between the root canal filling material and the root canal wall is improved, and the sealing properties are improved, but also the compatibility with the above-described component (A) is very good. Therefore, there gives rise to an effect that the actual production is easy. It is necessary that the content of the component (B) is 0.1 to 20% by weight. When the content of the component (B) is less than 0.1% by weight, the root canal filling material is liable to be broken during the filling operation. On the other hand, when the content of the component (B) exceeds 20% by weight, in the case where the root canal filling material is formed in a point-like state, the flexibility is excessively large, so that the point hardly reaches the root apex.
The paraffin wax as the component (C) is effective for imparting proper flexibility to the root canal filling material and making the filling operation easy. The component (C) is compounded in an amount of 0.1 to 10% by weight. When the content of the component (C) is less than 0.1% by weight, the plasticity is too low, so that the filling operability within the root canal is lowered. On the other hand, when the content of the component (C) exceeds 10% by weight, the root canal filling material is brittle so that it is liable to be broken.
The component (D) is one or two or more inorganic fillers selected from zinc oxide, barium sulfate, zirconium oxide, and titanium oxide, and imparts strength as well as radiopacity to the root canal filling material. The content of the component (D) is 30 to 95% by weight. When the content of the component (D) is less than 30% by weight, the hardness is lowered, and the radiopacity is insufficient. On the other hand, when the content of the component (D) exceeds 95% by weight, not only the root canal filling material is excessively brittle, but also the viscosity during the production is too high, whereby the productivity of the root canal filling material is lowered.
In the root canal filling material according to the present invention, so far as its characteristics are not lost, various inorganic or organic coloring agents or bactericides maybe used.
Next, the root canal filling material according to the present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.